A Fowl Dilemma

Image by "The Wanderer's Eye" via Flickr

Today, I will tackle the conundrum of Which came first:  the chicken or the egg? This is an age-old dilemma, confounding early philosophers.  The core argument takes the form of a catch-22.  All chicken hatch from an egg.  Hence, to have a chicken, one must first have had an egg.  But chicken eggs need to be laid by a chicken.  Hence, to have an egg, one must first have a chicken to lay it.  Phrased this way, this question does not seem to have a good solution.  Nevertheless, evolutionary biology has been able to resolve the issue with a correct but perhaps unsatisfactory answer.

The Solution

The answer to this question really depends on the phrasing and assumptions.  The quick answer is ‘Yes’.  The long answer is, predictably, long and complicated and requires a rudimentary understanding of evolutionary biology and speciation.

Inductive Reasoning

If we accept the reasoning presented in the introduction, we end up framing the problem in a very weird manner with no real satisfactory outcome.  This is because the problem is essentially stated in the form “x is needed for y” and “y is needed for x”.  One can try to work around this by saying that both the chicken and egg were always present – that there was no first chicken nor egg.  Unfortunately, while this solution works in an abstract philosophical argument, it isn’t very realistic.  The universe has an age (around 14 billion years) and so does the Earth.  The domesticated chicken evolved on earth quite recently.  Hence, any argument that posits the perpetual, eternal existence of chickens and eggs is really hard to accept.  Fortunately for us, modern biology has a much better answer.

Defining Species

The crucial difficulty with this problem is its phrasing and the underlying assumptions it tries to invoke.  An incorrectly framed question encourages us to work with a faulty mental model of the problem, leading us on tangents and down dead ends.  We need to come up with a better way of understanding the question.  To tease this out, let us go through a thought experiment.  What is a human?  What does it take to be a human?  Humans are not all the same.  We have difference weights, heights, facial structures, skin tones and abilities.  We all live for differing lengths of time.  We differ is such numerous and significant ways and yet, we are fundamentally human.  How different does one have to be to not be human?  Some people are born with too many or too few body parts.  Are they not human?  What does it take to belong to a particular species?  There is no clear formal definition as to what species are.  They are an artifact of our language and our early understanding of evolutionary biology.  Defining species is akin to defining intelligence.  One has a fairly good idea of what it is but formalizing it tends to reject cases that we might want to accept and accept cases that we might want to reject.

Nevertheless, we have a number of heuristics that can help us come up with a semi-working definition.  A common characteristic of organisms within a species is that they can interbreed.  Two humans can mate to produce a human offspring.  Two cows can do the same.  On the other hand, members of different species usually cannot interbreed.  Hence, cows cannot mate with horses.  In the rare cases for which this is possible, the offspring is usually either not viable (the offspring dies before reaching maturity) or sterile (unable to reproduce further).  For example, horses can mate with donkeys to produce mules, with the caveat that most mules are sterile and cannot sustain a mule population on their own.

Understanding Speciation

The Evolutionary History of Humans

Now that we have a vague understanding of what species are, let us try to attack the problem of speciation.  Speciation is the emergence of a new species from their predecessors.  A species of organisms doesn’t pop out of nowhere.  It usually evolves from a previous, genetically similar organism.  Humans and the other great apes diverged from a common ancestor a few million years ago.  How did this happen?  Why are there both humans and chimpanzees alive today?  To answer this, we need to think of species in terms of populations rather than in terms of individuals.  Suppose a portion of our common ancestor’s population were to become separated from the rest, either due to migration, exploration, natural disasters or some other similar reason.  The individuals in each population interbreed with each other and roughly maintain genetic compatibility.  But the two populations themselves are working under different conditions.  One may be in a hot climate and the other in a cold one.  One may have an abundance of food and the other, a scarcity of it.  One may have to avoid predators by hiding on trees.  The other may have no such tree cover and may have to fight predators on land.  These physical constraints (known as selection pressures) cause the two populations to evolve differently.  They adapt and acquire different characteristics.  If the two populations were still in contact, these acquired traits can then be intermixed between the two populations.  If the populations are separated for extended periods of time, the difference in traits that characterize each population will continue to build up, eventually causing the two populations to not be genetically compatible with each other.  This phenomenon is known as genetic drift and is caused due to the isolation of one population of a species from another.  After enough time, the two populations are so different that they are now considered separate species.  In the case of our common ancestor, the human and chimpanzee populations evolved separately to create the species that we see today.  The modern human itself is one species out of many competing species such as Neanderthals that evolved from the early human ancestor population.

Chickens Everywhere

Now to attack the question at hand.  What came first?  The chicken or the egg?  The question, it turns out, has no particularly good answer.  There was no one prototypical chicken that mothered all the modern chickens that we see today.  Chickens diverged from an ancestor (probably some form of wild fowl) and eventually became domesticated.  This was to a population as a whole and not to any single individual organism.  If I gave you one grain of rice, you would call it exactly that – a grain of rice.  If I gave you 10, you would consider it a few grains of rice. If I kept adding rice, one grain at time, there will eventually come a point when you would consider it a heap of rice.  When does that happen?  When do we start referring to a quantity of rice as a heap of rice?  If I took a heap of rice and took away a grain, is it no longer a heap of rice?  Similarly, what does one mean when one asks for the first chicken?  The chicken’s parents were only very slightly genetically different from the chicken itself.  Are they not chickens?  Is there a way for everyone to agree on where the starting point is and where to draw the line?  As you can now understand, the answer is one of definition and not one of understanding.  We perfectly well understand how populations evolve.  We perfectly well understand that anything that is considered a modern chicken must have hatched from an egg.  What we can’t agree on is when chickens stop being chickens.  All we can say is that, based on some arbitrary definition, there was a first chicken which satisfies that definition whose parents didn’t.  If that definition happens to allow for the characteristics of the egg in which it was hatched, then the egg came first.  If not, then the chicken came first.